A turbomachine, in particular a gas turbine, has a turbine in which hot gas, which has previously been compressed in a compressor and heated in a combustion chamber, is expanded in order to perform work. For high mass flows of the hot gas and therefore for high power output ranges of the gas turbine, the turbine is designed in an axial type of construction, the turbine being formed by a plurality of blade rings lying one behind the other in the through-flow direction. The blade rings have moving blades and guide vanes arranged over the circumference, the moving blades being fastened to a rotor of the gas turbine and the guide vanes being fastened to the casing of the gas turbine.
The thermodynamic efficiency of the gas turbine is the higher, the higher the inlet temperature of the hot gas into the turbine is. By contrast, limits are placed upon the thermal load-bearing capacity of the turbine blades. It is therefore desirable to provide turbine blades which, despite as high a thermal load as possible, have mechanical strength sufficient for the operation of the gas turbine. For this purpose, appropriate materials and material combinations are available for the turbine blades, but, according to the current state of the art, allow only inadequate exploitation of the potential for increasing the thermal efficiency of the gas turbine. For a further increase in the permissible turbine inlet temperature, it is known to cool the turbine blades during the operation of the gas turbine, with the result that the turbine blade itself is exposed to lower thermal load than would be the case without cooling because of the thermal load caused by the hot gas.
In order to keep the temperature of the turbine blades low, the blades are cooled, for example, by means of film cooling. For this purpose, the blades are provided on their surface with a plurality of cooling air holes, via which cooling air is transported from the blade interior to the surface of the turbine blades. After the cooling air has left the cooling air holes, it flows in the form of a film along the surface of the turbine blade and thus insulates the surface of the turbine blade from the hot gas. Furthermore, the film acts as a barrier, so that transport of the hot gas to the surface of the turbine blade is suppressed.